The present invention relates to a front-passenger-seat airbag apparatus for protecting an occupant sitting on a front passenger seat and its setting structure for installing the airbag apparatus on the backside of an instrument panel.
In a conventional airbag apparatus for a front passenger seat, a folded airbag is accommodated in a container-like casing (i.e., a retainer) and the front opening of the container is covered with a lid. The container is provided with an inflator or gas generator for inflating the airbag arranged therein. The lid may be a lid-like member arranged differently from the instrument panel or may be a region of the instrument panel defined by a tearing line.
A general structure of the airbag apparatus for a front passenger seat having the lid in the region of the instrument panel will be described below with reference to FIG. 7. FIG. 7 is a sectional view showing a conventional airbag apparatus for a front passenger seat and a setting structure thereof in an instrument panel.
The airbag apparatus 100 for a front passenger seat shown in FIG. 7 includes a container 101 having a substantially rectangular shape in plan view, an airbag 102 folded and housed within the container 101, an instrument panel 103 covering an opening on the upper surface of the container 101, a plate 104 interposed between the opening of the container 101 and the instrument panel 103, and a substantially cylindrical inflator 105 for generating gas to inflate the airbag 102.
On the backside of the instrument panel 103, a tearing line (a weakened or fragile portion) 103a is formed. With this tearing line 103a, a region of the instrument panel 103 is partly defined as a lid for covering the opening of the container 101.
The plate 104 is arranged adjacent to the backside of the instrument panel 103 along the region of the instrument panel 103. The plate 104 is configured integrally with the instrument panel 103 and has a connecting piece 104a formed in the peripheral portion of the plate 104 for connecting the container 101 to the instrument panel 103.
On the bottom of the container 101, a semi-circular arc-shaped inflator-accommodating member 106 is arranged, and the inflator 105 is fitted into the accommodating member 106 and a capping member 107 is covered from above on the inflator 105. The capping member 107 has flanges 107a overlapping the bottom surface of the container 101 so that peripheral portions of a gas inlet of the airbag 102 are clamped with between the flanges 107a and the bottom surface of the container 101. The flanges 107a and the accommodating member 106 are integrally fixed to the container 101 with bolts and nuts.
In the periphery of the opening of the container 101, a fixing member 108 used to be fixed to the above-mentioned connecting piece 104a is arranged. The fixing member 108 is provided with an extended portion 108a extending from the external peripheral surface of the container 101 along the bottom surface of the connecting piece 104a, and the extended portion 108a is provided with insertion holes (not shown) formed for inserting bolts or rivets.
The container 101 having the airbag 102 folded and accommodated therein is positioned on the region as the lid from the backside of the instrument panel 103. The extended portion 108a of the fixing member 108 arranged in the periphery of the opening of the container 101 is overlapped with the connecting piece 104a so that the container 101 and the instrument panel 103 are connected together with the connecting piece 104a and the extended portion 108a connected with bolts 108b and nuts 108c. 
However, in such an airbag apparatus 100 for a front passenger seat, the container 101 is firmly fixed to the connecting piece 104a along the entire periphery of the opening by the fixing member 108 arranged in the periphery of the opening of the container 101, so that it is difficult to remove the container 101 relative to the instrument panel 103. In particular, it is extremely difficult to release the connection between the bolt 108b and the nut 108c disposed adjacent to a windshield (on the front side of a vehicle body).
Another airbag apparatus, wherein even in a state that the instrument panel is attached to a vehicle body, the container is detachable, is described in Japanese Unexamined Patent Application Publication No. 2001-322523.
FIG. 4 is a longitudinal sectional view of an airbag apparatus for a front passenger seat showing the airbag apparatus for a front passenger seat and its setting structure to an instrument panel according to Japanese Unexamined Patent Application Publication No. 2001-322523; FIG. 5 is a perspective view of the airbag apparatus for a front passenger seat viewed from the upper surface of part of the container; and FIG. 6 is a sectional view showing the engaging relationship between the container part of the airbag apparatus for a front passenger seat and the instrument panel.
This airbag apparatus 1 for a front passenger seat includes a container 2 having a substantially rectangular shape in plan view, an airbag 3 folded and housed within the container 2, a substantially cylindrical inflator 4 for inflating the airbag 3, an instrument panel 5 covering an opening on the upper surface of the container 2, and a plate 6 interposing between the container 2 and the instrument panel 5 and connecting between the container 2 and the instrument panel 5.
On the backside of the instrument panel 5, a tearing line 5a is formed. The instrument panel 5 is provided with a wall portion 7 extending downward along one side face of the container 2. The wall portion 7 is provided with an engagement portion 8 constituted of an opening.
A portion of the plate 6 overlapping with the engagement portion 8 has insertion holes 9 used for inserting retainer members 15 into the engagement portion 8. From an edge of the plate 6 opposite to the wall portion 7, a connecting piece 10 extends for connecting the container 2 to the instrument panel 5. The connecting piece 10 is provided with stud bolts 10a. 
The plate 6 has a cleavage section 6a formed at the same position as the tearing line 5a and a hinge (not shown) disposed in the vicinity of the peripheral edge of the plate 6 for rotating the plate 6 like a door. Thereby, when the airbag 3 is inflated so as to push the instrument panel 5 through the plate 6, the plate 6 is cleaved together with the above-mentioned region of the instrument panel 5 and is pushed open toward a vehicle cabin integrally with the region of the instrument panel 5.
On the bottom of the container 2, a semi-circular arc shaped inflator-accommodating member 11 is arranged, and the inflator 4 is fitted into the accommodating member 11 and a capping member 12 is covered from above on the inflator 4. The capping member 12 has flanges 12a overlapping the bottom surface of the container 2 so that peripheral portions of a gas inlet of the airbag 3 are clamped with between the flanges 12a and the bottom surface of the container 2. The flanges 12a are fixed to the container 2 with bolts 13 and nuts 14.
One side of the container 2 extending in the longitudinal direction is provided with the retainer members 15 for engaging with the above-mentioned engagement portion 8. Each of the retainer members 15 includes a connection section 15a connected to the container 2 along the one side and a hook 15b extending from the top of the connection section 15a toward the outside of the container 2 so as to be inserted into the engagement portion 8 with the end portion bent downward along the wall portion 7.
The other side of the container 2 opposite to the above-mentioned one side is provided with fixing members 16 to be fixed to the connecting piece 10 of the plate 6. Each of the fixing members 16 includes a connection section 16a connected to the container 2 along the opposite other side and an extended section 16b extending from the top of the connecting piece 10 toward the outside of the container 2 along the connecting piece 10. The extended sections 16b are provided with insertion holes 16c arranged for inserting the stud bolts 10a of the connecting piece 10.
Upon setting the container 2 in the instrument panel 5, at first, the hooks 15b of the retainer members 15 are inserted into the insertion holes 9 and the engagement portion 8 so that the retainer members 15 is brought into engagement with the engagement portion 8 so as to arrange the one side of the container 2 along the wall portion 7. Then, the extended sections 16b of the fixing members 16, which are provided in the other side opposite to the one side of the container 2 arranged along the wall portion 7, are overlapped with the connecting piece 10 of the plate 6. As a result, the stud bolts 10a are inserted into the insertion holes 16c so as to fix the fixing members 16 to the connecting piece 10 by tightening the nuts 10b from the top end of the stud bolts 10a protruding from the insertion holes 16c toward the bottom surface of the extended sections 16b. 
In the airbag apparatus 1 for a front passenger seat and its setting structure constructed as described above, upon setting the container 2 in the instrument panel 5, the side of the container 2 arranged adjacent to a windshield (on the front side of a vehicle body) is attached to the instrument panel 5 with a simplified structure of only the engagement between the locking member 15 and the engagement portion 8, so that the removing of the container 2 from the instrument panel 5 can be easily performed by releasing the fixing of the fixing member 16 arranged in the other side of the container 2 to the connecting piece 10 and by extracting the locking member 15 from the engagement portion 8. As a result, for example, in a state that the instrument panel is kept attached to the vehicle body, the removal of the container can be easily accomplished for maintenance.
However, in the conventional airbag apparatus for a front passenger seat and its setting structure described above and shown FIGS. 4 to 6, after the stud bolts 10a are inserted into the insertion holes 16c, during screwing the nuts 10b to the stud bolts 10a, the instrument panel 5 is liable to escape upward so that there is a slight problem in the tightening operation of the nuts to the stud bolts 10a. 